For most of the comparison methods, we use the codes from [1]} for implementation. For a particular hyper-parameter configuration, we follow the similar protocol used in [2]}. The target domain is partitioned in validation and test sets. The validation set is used to obtain the best accuracy in the range of the possible hyper-parameters. The hyper-parameter range used follows [3]} and we slightly reduce the range to fit our task. With the best selected hyper-parameters, we evaluate the performance on the testing set. Classification accuracy on the target domain is adopted as the evaluation metric.
